Vitamin A For Horses

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Vitamin A is a fat-soluble vitamin that is essential for growth and development, immune function, and reproductive health. It is commonly found in foods such as fruits, vegetables, whole grains and dairy products. In the case of horses, however, the most important source of vitamin A is beta-carotene.

Beta-carotene is a precursor to vitamin A and is found in green leafy vegetables such as spinach or kale. These vegetables also contain other nutrients that are beneficial to horses including fiber and antioxidants.

Horse owners who feed their horses a diet rich in beta-carotene will notice an improvement in their horse’s coat quality as well as increased energy levels and stamina during exercise.

Vitamin A For Horses

Q: I bought a multivitamin supplement for my horse, and when reading the ingredients list, I noticed it contains an extremely high dose of vitamin A, 100,000 IU per pound. Could this be a misprint or do horses need such high levels of vitamin A? I know in humans an overdose of vitamin A can cause serious illness.
Name withheld by request

Eleanor M. Kellon, VMD

A: Vitamin A (trans-retinol) is an essential nutrient, critical for normal vision (night and color vision), immune function, gene action, fertility and development of the fetus, normal bone metabolism, red-blood-cell production, normal skin/hoof/eye surfaces and is also an antioxidant. Vitamin A is stored in the liver. Because it is one of the most-studied vitamins, it is found in a wide variety of feeds and supplements.

Vitamin A per se does not exist in plants. Plants contain carotenoids, which the horse’s body can convert into vitamin A. The major carotenoid in forage is beta-carotene. Fresh, nondormant pasture grasses have the highest concentration, old grass hays the lowest. While beta-carotene from forages is easily converted into vitamin A, supplemental forms are not as efficiently used. For this reason, supplemental forms are usually stabilized forms of vitamin A itself, such as retinyl palmitate or retinyl acetate. That is what you will see on the ingredients list.

The vitamin A requirement of adult horses at maintenance is 30 IU/kg (1 kg equals 2.2 pounds) of body weight. For growing and exercising horses, it is 45 IU/kg of body weight. A 500-kg (1,100-pounds) horse would therefore need 15,000 IU of vitamin A per day at rest and 22,500 IU per day when working. The proposed upper safe limit of intake is around 160,000 IU per day for a 500-kg horse.

Vitamin A can be toxic because excesses will accumulate in the liver. Toxicity includes bone fragility; developmental orthopedic disease in growing horses; areas of abnormal bone growth; itching, peeling skin and birth defects. Symptoms of bone disease include swelling, pain and fractures. The only treatment is to stop feeding vitamin A. 

The amount you need to supplement depends entirely on how much is already in your horse’s diet. As mentioned, fresh grass is rich in vitamin A precursors, and horses on pasture do not need any supplemental vitamin A.

According to figures published by the National Research Council, alfalfa hay contains almost 25,000 IU of vitamin A per kg, which exceeds the total daily requirement of vitamin A for all classes of horses.

Grass hays are more variable. Canary grass was reported as 6,762 IU/kg, orchard grass as 13,366 IU/kg and timothy as 18,700 IU/kg. Even for the lowest figure—canary as 6,762 IU/kg—it would take only 3.3 kg or 7.3 pounds of hay to meet even the upper-level daily requirements.

However, vitamin A in stored forage/hay does decrease over time. By the time hay is 12 months old, the vitamin A content has decreased to one-half to one-third of the original pasture level. Hay that is 24 months old will have only about one-tenth of its original vitamin A content. A good rule of thumb is that if the hay has a nice green color, it contains adequate vitamin A.

Virtually all bagged feeds are also fortified with vitamin A, containing from 3,000 to 5,000 IU/lb. Balancer-type vitamin A and mineral supplements may contain as much as 36,000 IU/lb. The horse can therefore easily meet or exceed his vitamin A requirement with these products. How much is too much in a supplement depends both on the amount contained per dosage and how much your horse actually needs. If you are feeding only old hay and no supplemented grain, your horse may well need vitamin A. Otherwise, you may be more likely to overdo it rather than require it.

Eleanor M. Kellon, VMD, is a 1976 graduate of the University of Pennsylvania Veterinary School. Co-owner of the Equine Cushing’s and Insulin Resistance Group, she has written several books and thousands of magazine articles on equine nutrition and health. She also teaches online equine nutrition and care courses (drkellon.com

what does vitamin e do for horses

Vitamin E is a fat-soluble vitamin that acts as an important antioxidant for horses. It helps maintain a healthy immune system and supports normal nerve and muscle function.

Horses need vitamin E in their diet because they cannot synthesize it endogenously in their body. It is found in fresh, green grasses and forages. Horses that are mostly on lush pasture will get enough vitamin E by grazing fresh grass.

Cutting grasses and forages to harvest hay causes rapid degradation of vitamin E that continues as the hay is stored. Hay stored for longer periods of time or poor-quality hay will have lower vitamin E content. If your horse is fed mostly hay, they likely have low vitamin E intake.

Vitamin E deficiency in horses can cause them to be more likely to tie-up after exercise. They might be sick with frequent coughs and colds and recover slowly. Insufficient Vitamin E in the diet can make some equine neurological disorders worse.

Mad Barn’s Omneity Premix is a fully balanced equine mineral and vitamin supplement that provides comprehensive nutritional coverage for your horse’s needs. It contains 8,500 IU per kg Vitamin E (dl-alpha-tocopherol), sufficient to meet the needs of most horses.

We also carry bulk natural Vitamin E powder (405,000 IU per kg) for horses that require higher levels.

Vitamin E and selenium are necessary for optimal antioxidant protection because they support the function and formation of glutathione peroxidase, the main antioxidant enzyme found in all cells of the body. Mad Barn’s Natural E/ Organic Se pellet provides both of these key nutrients in natural, organic forms with high bioavailablity.

Vitamin E Supplement for Horses

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  • Optimal antioxidant protection
  • Supports exercise recovery
  • Supports immune function
  • Natural with high bioavailability

Why Horses Need Vitamin E

Vitamin E is a shared term used to encompass eight compounds – tocopherols (saturated) and tocotrienols (unsaturated). Tocopherols and tocotrienols have four structural variants called alpha, beta, gamma, and delta. Alpha-tocopherol is the most abundant and most bioavailable in horse feeds.

Antioxidants like vitamin E protect cells from free radicals. Free radicals are unstable molecules that steal electrons from other molecules to become stable, causing the other molecules, like DNA and cell membranes, to become unstable.

Free radicals are naturally produced when horses metabolize carbohydrates, fat, or protein to make energy. Free radicals are not completely bad. A small amount are needed to help cells respond to signals in the body.

However, too much free radical damage, called oxidative stress, damages cells often to the point of cell death. This will cause organs and tissues like the liver and muscles to not function properly and negatively impact the horse’s health, resulting in premature aging.

Antioxidants are compounds that neutralize free radicals before they cause damage. Antioxidants come in many forms. Vitamins (vitamin E and C), minerals (selenium) and enzymes (glutathione peroxidase) all work together to provide optimal antioxidant protection.

Oxidative damage from having low antioxidant status or high free radical burden can present itself in horses as muscle soreness after exercise, slow recovery from illness, or frequent illness.

Feeding adequate amounts of Vitamin E and other natural antioxidants can ensure your horse has appropriate antioxidant defense. Getting enough of this vitamin in the diet is particularly important for equine athletes.

Vitamin E Benefits for Horses

Below are the top 8 benefits of vitamin E in horses:

  1. Vitamin E eases muscle soreness and stiffness in exercising horses, helping them sustain high levels of activity.
  2. Having adequate intake of this vitamin will help muscles recover after exercise which can support athletic performance.
  3. Horses with adequate vitamin E intake are less likely to experience chronic tying up (exertional rhadomyolysis).
  4. Vitamin E boosts the immune response, enhancing the bacteria killing capacity of immune cells. This helps horses recover from illness quickly.
  5. Vitamin E can help horses with insulin resistance. According to Dr. Nicholas Frank at the University of Tennessee, daily intake of 1000 IU could help improve insulin sensitivity.
  6. Having adequate antioxidant defenses can minimize stress and health issues related to travel and competition, helping your horses stay healthy and ready to compete.
  7. It can prevent or minimize the effects of neurological disorders like equine motor neuron disease (EMND) and equine degenerative myeloencephalopathy (EDM) from developing.
  8. Horses with polysaccharide storage myopathy (PSSM), also known as equine polysaccharide storage myopathy (EPSM) have a higher burden of oxidative stress. Vitamin E could help horses with this muscular disorder.

Vitamin E Research Results

Supplementation for Exercise Recovery

A study by Fagan et al., 2017 examined the effect of vitamin E supplementation on oxidative stress in exercising horses. They studied natural and synthetic forms of vitamin E at two different doses.

After 6 weeks, horses receiving 4000 IU per day of natural vitamin E (d-alpha-tocopherol) had lower serum AST (aspartate aminotransferase) than those fed 4000 IU or 1000 IU per day of synthetic vitamin E. Serum AST is an indicator of muscle damage in horses. When levels of this marker are lower in the blood, it means horses experience less muscle damage.

The natural vitamin E also resulted in lower TBARS (thiobarbituric acid-reactive substance) which suggests they had less oxidative damage. Horses on natural vitamin E also had improved stride duration compared to those on the synthetic form.

This study shows that Vitamin E, particularly in its natural form, helps equine athletes sustain high levels of activity by reducing oxidative damage and minimizing muscle damage.

In another study, horses used for police service in Brazil were fed 2.8 mg selenium and 2,000 IU vitamin E (doses for a 400 kg horse). Their response to exercise was assessed before and after 30 days of supplementation.

After supplementation, horses were better adapted to exercise because they had less of the stress hormone cortisol. They also had improved energy metabolism as indicated by less lactic acid in the blood.

Enhanced Immune Function

A study involving older horses ranging from 7 to 26 years old found that natural Vitamin E had an immune enhancing effect.

In the study, horses in the treatment group were fed natural vitamin E (alpha-tocopheryl acetate) for 16 weeks at a dose of 15 IU/kg of bodyweight. This is equivalent to a dose of 7500 IU for a 500 kg horse. Compared to horses in a placebo group not receiving any treatment, those horses given Vitamin E experienced improved immune function.

Specifically, the study showed that horses given vitamin E produced more antibodies after vaccination against West Nile virus. In addition, the ability for their immune cells to fight off bacteria was enhanced.

Vitamin E supplementation to improve immune function is especially beneficial to older animals because immune function naturally declines with age.

Vitamin E Requirement in Horses

The National Research Council (NRC 2007) recommends a minimum daily intake of 1-2 IU per kg body weight. For a 500kg horse at maintenance the daily intake should be 500 to 1000 IU. This is easily met if horses have frequent access to fresh grasses and forages in pasture. Grazing on pasture provides approximately 2,000 IU per day[5]

The vitamin E requirement increases to a minimum of 1000 IU per day in working horses and pregnant or lactating broodmares. Weanlings and yearlings require 500-750 IU Vitamin E per day.

It is important to note that NRC levels are not necessarily reflective of optimal Vitamin E intake and are merely the minimum required to prevent a deficiency. In many cases, feeding higher amounts of this vitamin can improve health and well-being.

The body condition of your horse might also determine how much vitamin E to provide. Skinny horses have less fat tissue to store vitamin E so they will require more in their diet, around 1500-2000 IU per day.

Higher levels can also be provided to horses with allergies, metabolic syndrome, that are frequently ill or recovering from illness. Daily doses up to 10,000 IU have been shown to be safe in horses.

Horses on pasture during the summer can build up stores of vitamin E in their liver, muscle and adipose (fat) tissue that they can use during winter months when they no longer have access to fresh grass or forages. However, this may not be sufficient to meet their daily requirement and optimize health.

Vitamin E Sources

Consult with an equine nutritionist to determine whether your horse needs additional Vitamin E in their diet. You can check your horse’s diet online using our diet analysis tool and our equine nutritionist will be happy to provide you with feed.

If you determine that your horse needs more Vitamin E, you can increase dietary consumption by allowing more access to lush pasture.

Keep in mind that fresh pasture might have high sugar content which could be a concern for overweight or insulin resistant horses. Magnesium levels of grasses in springtime and laminitis should also be taken into account.

To minimize loss of vitamin E from hay, cut it early in the season and store it in a dry, dark place. Sunlight and moisture are the main factors that contribute to vitamin E degradation from feed. In one study, alfalfa hay lost 50% of its vitamin E content over one month of storage. Also, earlier cuts of alfalfa hay have higher levels of vitamin E than later ones. [3]

Absorption of vitamin E is enhanced by fat in the diet. If you are interested in feeding supplemental vitamin E you may want to consider Mad Barn’s W-3 oil which is enriched with Vitamin E. A daily dose of 100 mL W-3 oil provides 400 IU natural vitamin E. Daily total fat intake should not exceed 8% for equine diets.

w-3 Oil Essential Fatty Acid Supplement

W-3 OIL

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  • Promotes joint comfort
  • Helps to fight inflammation
  • Skin & coat condition
  • Palatable source of Omega-3’s

Like all fat-soluble vitamins, excess vitamin E is stored in the body, mainly in the liver and in fat tissue. Toxicity can occur with overfeeding vitamin E; however, this is unlikely in horses.

High vitamin E intake can interfere with absorption of vitamin A. The fat content of the diet can also influence vitamin E absorption.

As with all vitamins and minerals, it is important to consider the whole diet to ensure there are no imbalances that can affect the absorption or function of vitamins and minerals. Submit your diet for analysis online and our equine nutritionist can help you review any potential changes to your feeding program.

Natural vs Synthetic Vitamin E

Although there are eight forms of vitamin E, most supplements for humans and animals contain alpha-tocopherol. When supplementing this vitamin, it is important to choose natural forms because it can be used much more readily by the horse’s tissues.

Natural forms are typically listed with a “d” prefix, like d-alpha-tocopherol, d-alpha tocopheryl acetate or d-alpha tocopheryl succinate. Synthetic vitamin E supplements will have “dl” as the prefix, such as dl-alpha tocopherol.

Absorption of natural and synthetic vitamin E is the same. However, the ability for tissues to use vitamin E is much greater with natural vitamin E than synthetic.

Mad Barn’s Natural E/Organic Se and Vitamin E supplements as well as AminoTrace+ all contain natural forms of vitamin E d-alpha-tocopherol.

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